This invention relates to power line disturbance analysis and more particularly to arrangements for reporting the most significant transient impulses occurring within a predetermined monitoring interval.
Equipment for reliably indicating parameters of line voltage disturbances has, however, heretofore been made widely available. For example, it has for some time been practical to monitor 60 Hz mains and to record the time of occurrence and the peak value of a transient impulse, the number of cycles of the mains frequency during which a line voltage sag or surge persisted, and the slow-averaged RMS level of the line voltage. Instruments are avaliable which have the ability to store data concerning a limited number of transients that may occur while the outprinting equipment is operating, and when the capacity of this temporary memory is exceeded, to printout a summary count of the number of excess transients and of the highest amplitude reached by any of the excess transient disturbances. The Dranetz Engineering Laboratories' Model 606 "Power Line Disturbance Analyzer" is an example of such presently available equipment.
While instruments which record the occurrence of significant transient disturbances by indicating those of highest amplitude in the monitoring interval are indeed useful, it is apparent that not all high amplitude disturbances may exhibit sufficient energy content to be of importance. As is well-known, the energy content of a voltage impulse, for example, is a function not only of amplitude but of time duration as well. The volt-second "area" of a transient impulse is therefore an approximate indication of the energy content of the voltage disturbance. Readily available operational amplifiers which perform an integration operation may accordingly conveniently be employed to indicate the volt-second area of impulses of various types.
The incorporation in power line disturbance analyzing equipment of an operational amplifier to indicate impulse energy content, while obviously useful for the foregoing reason, does, however, pose certain problems. It would, of course, be desirable to provide some minimum amplitude threshhold below which transient impulses could be ignored and, as disclosed in the copending application of P. P. Cox entitled "Dynamic Threshhold Impulse Directivity Indicator" Ser. No. 879,234 filed of even date herewith, it may be advantageous in transient analyzing circuits to increase the nominal or user-set threshhold in accordance with the peak magnitude actually exhibited by a prior pulse occuring in the monitoring interval so that only pulses of greater amplitude, if any should thereafter occur in the interval, will be recorded.
While increasing the threshhold in this manner is effective to screen out all but the largest impulse of interest it is equally to be desired to avoid the "over-reporting" of such an impulse. Unfortunately, high amplitude transients sometimes induce a ringing effect in the power line which persists after the initiating transient has subsided. It would be advantageous to discriminate against reporting the volt-seconds "area" of the trailing ringing pulses.